This invention relates to a method of preparing a purifying agent for efficiently purifying pulp waste water, waste water from dyeing factories and other industrial waste waters by activating highly siliceous porous mineral substances such as diatomaceous earth or foamed perlite by baking it at a temperature of from 100.degree. to 500.degree.C, preferably from 250.degree. to 350.degree.C, thereby imparting to the substances the properties of coagulation and decolorization in addition to their inherent properties of dehydration and filtering.
Similar to waste gas, industrial waste water is a source of serious public hazard and conventional methods of processing industrial waste water include chemical biological methods and a method of utilizing active carbon. However, all of these prior art methods are not sufficiently efficient, especially they can not effectively decolorize.
Heretobefore, use of diatomaceous earth and foamed perlite has been limited to auxiliary filtering material or filler for processing industrial waste water and the method of processing diatomaceous earth and foamed perlite has been limited to the pickling treatment for removing clay, organic substances and soluble salts which are contained in these materials and to the baking treatment for the purpose of imparting thereto suitable strength and hardness which are necessary for the filtering material or the baking treatment at high temperatures for foaming.